Short answers, pulled from the story.
Robert Oppenheimer published a paper showing that calculations in quantum electrodynamics always resulted in infinite quantities in 1930. These infinities appeared as electron self-energy and vacuum zero-point energy for both electrons and photons.
Julian Schwinger, Richard Feynman, Freeman Dyson, and Shinichiro Tomonaga developed a systematic procedure called renormalization around 1950. This method replaced calculated values of mass and charge which were infinite with their finite measured values.
Carl David Anderson discovered evidence for positrons in cosmic rays in 1932. This discovery confirmed Dirac's 1929 proposal that particles with the same mass as electrons but opposite electric charge existed.
Gerard 't Hooft proved non-Abelian gauge theories were renormalizable in 1971. This proof resolved issues with earlier versions of the theory developed by Sheldon Glashow, Abdus Salam, and John Clive Ward.
The Higgs boson was finally detected in 2012 at CERN. This detection marked complete verification of existence for all constituents of the Standard Model including electroweak theory and chromodynamics.